Ovarian Activity in the Pregnant Mare

Abstract

OVARIAN activity in the mare in early pregnancy presents some unusual features which are inconsistent with the accepted normal behaviour of the mammalian gonad during gestation. In the first place, the corpus luteum of pregnancy is very shortlived, and unlike that of most other mammals its period of activity would not seem to be prolonged much in excess of that of the oestrous cycle of the non-pregnant animal. Harrison¹ has observed that the corpus luteum of pregnancy completely fills the cavity of the ruptured follicle in four to six days and attains maximum size by the tenth to fourteenth day. Regression is stated² to occur at about the end of the first month. Secondly, follicular development is a common feature of ovarian activity at this time, and Day³ has observed the occurrence of ovulation in a mare on the twenty-third day of pregnancy. Ovarian activity reaches its peak during the second and third month of pregnancy, when gonadotrophic hormone is abundant in the blood.